Novel yarn like structures from extruded thin walled tubing



United States Patent 3,135,813 NOVEL YARN LTKE STRUCTURES FROM EX- TRUDED THIN WALLED TUBING Raymond Holden Speakrnan, Harrogate, England, assignor to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain No Drawing. Filed May 25, 1962, Ser. No. 197,612 Claims priority, application Great Britain May 29, 1961 5 Claims. (Cl. 264-269) This invention relates to novel shaped yarn like structures made from fibre forming synthetic linear polymers. It is known to spin hollow or lacunose filaments by introducing gases into annular spinneret orifices, but these filaments have a wall thickness not much less than the external radius of the filaments. A process is also known for producing filaments comprising drawing an organic thermo-plastic high polymer in the form of a narrow strip or tube through a slot which is narrower than the width of the strip or tube to be drawn. The tubes or strips so produced may have a Wall thickness of or less, e.g. There is no suggestion of introducing a defined volume of gas into the tube.

1 have now found that in order to make yarn like structures which may be used for textile applications where soft handle is required and where therefore the stiffness due to the known thickness of the strips or tubes cannot be tolerated, it is necessary to reduce this thickness to not exceeding 8 microns and preferably not exceeding 5 microns.

Fabrics from yarns made with such very thin films exhibit similar flexibility to those from conventional multifilament yarns. In normal multi-filament fabrics this flexibility is achieved by the individual filaments in the yarns spreading into a ribbon so as to form a flexible hinge, substantially one filament thick, whereas our novel yarn like structures obtain a similar hinge effect by the planes of the films reorienting themselves at bends, so as to form similar flat hinges.

According to my invention 1 provide a process for the manufacture of novel shaped yarn like structures from fibre-forming synthetic linear polymers, comprising extruding or melt spinning the polymer in the form of a thin Walled tube, e.g. through a substantially annular aperture, introducing a gas supply into the tube, i.e. within the annulus, to control the diameter of the tube until solidification has occurred, characterised in that the dimensions of the annulus and the rate. of introduction of the gas are so related to wind up speed and final desired denier of the structure, that the wall thickness should not exceed 8 microns. Ths may be achieved if during the spinning process the gas contained within any finite section or portion of the tube is of substantially the same volume as that contained within any other section or portion of the tube of the same total weight as the said first section, due allowance being made for variation of temperature and further expansion of the gas during the process. It will be appreciated that the sections or portions referred to above will be of very different lengths, diameters and wall thicknesses due to the stretch occurring between extrusion and wind-up, but as it has been stipulated, two sections or portions of equal weight still contain equal volumes of gas. Generally air is introduced into the annular spinneret at such a rate that, after solidification, no inflation of the tube to a diameter greater than that of the 3,135,813 Patented June 2, 1964 annular spinneret aperture takes place, but at a rate suflicient to prevent undue contraction of the tube which in turn would cause the internal walls to come in to contact, prematurely. The structure may now be wound up and if desired the tube may be collapsed by pulling it through a narrow circular or shaped guide or die and/ or a loaded nip before forwarding or collecting the yarn like product, e.g. by winding on a bobbin. It will be appreciated that to permit this operation the contained gas should be allowed to escape, e.g. by perforating or slitting the tube. The tube is preferably oriented i.e. the birefringence of the melt spun tube is increased; this may be done by winding or forwarding the tube'at high speeds, using fluid, liquid or even mechanical drag forces. Alternatively or additionally the tube may be drawn to several times its length as spun, between feed rolls and faster rotating draw rolls, until a desirable orientation and birefiingence is obtained. Such orientation may be carried out before or after the collapsing of the tube. This thin wall tube provides a yarn like novel structure which possesses the desirable flexibility of a multifilament yarn but has novel properties of increased opacity, covering power, improved dyeability and which may be woven without the need for conventional twisting and sizing operations.

Synthetic fibre forming polymers which are suitable for use in my invention should have the property of being capable of being cold-drawn, such as nylon, polyesters and copolyesters based on terephthalic acid, e.g. polyethylene terephthalate, and stereospecific polypropylene. Longitudinal drawing of the tube brings about orientation and imparts strength and other desirable mechanical properties.

It will be understood that the total denier of the yarn like structure produced by this process is controlled, as in conventional spinning, by the relation between rate of pumping molten polymer through the annular aperture and the linear feed rate at which the product is wound up. The uncollapsed diameter of the tube, and hence the wall thickness is controlled by the supply of gaseous medium to the inside of the tube. For example, a denier tube of drawn polyethylene terephthalate of uncollapsed diameter of .050" would have a wall thickness of approximately 2.5 microns.

Our novel yarn like structure is characterised by a substantially tubular collapsed shape, having a wall thickness not exceeding 8 microns, preferably less than 5 microns but which may be as little as 1 micron, with a circumferential length corresponding to conventional yarn deniers, e.g. 25-150 denier, or more if desired, in its drawn condition.

If desired, the nip for collapsing the tube may be arranged to carry sharp projections so that a series of perforations are inserted in the tube. The perforations assist in penetration of after-treating liquids such as dyes or adhesives. It may be similarly arranged for the same purpose for the tube to be continuously slit into a multistrip filament throughout its length. It will be appreciated that good performance can be achieved if e.g. the extrusion temperature is set at the appropriate figure, determined by spinning experience with multi-filament yarn for the selected polymer.

The following examples illustrate but do not limit our invention.

Polyethylene terephthalate of intrinsic viscosity 0.67 is melt spun using an annular spinneret of /s"% in diare wound up without heating. The following table sets out the conditions and summarises the wall thickness of the tubes obtained. Experiment 6 results in a desirable yarn like structure having a wall thickness of 4.5 microns.

Spinning Spun tube spinneret Annu- Temper- Air Annulus lus ature Input I diameter Width (Dow 00.1 Internal Wall (ins) (ins) therm), mm. Diameter thickness 290 '22 0.015 0.0015 290 37 0. 020 0.0012 290 40 Instability (see below) 290 60 v 0.025 0.009 290 100 Instability (see below) 286 270 0.054 1 0.0045- 286 400 Instability|(see below) The instability referred to above takes the form of a series of bubbles of the order of 1 diameter along the hollow tube and spaced substantially at regular intervals of the order of-l to feet depending on air input. The bubbles are connected by an unbroken hollow tube, but because of its size, the tube cannot be wound up on con ventional winding equipment, but can be collected in a container such as a can, as it falls under gravity. The instability occurs when surface tension forces in the molten threadline or tube, whichtends to contract in diameter, will no longer allow an increase in air input to be carried down the tube, as a result swelling into a bubble of air immediately below the spinneret annulus where the extruded polymer is at its highest temperature and therefore lowest viscosity.

Having now established by experiments and with the aforementioned limitations, the following calculation of spinneret annulus diameter can be made:

Let spun denier required be w grams/ 9,000 metres Let desired wall thickness be tmicrons Let spun yarn density be d grams/ cc.

Let tube, diameter be .9 microns Then weight of 9,000 m.=w grams=d1rst 9 10 hence volume of air contained in one mg. of spun tube at w Wlnd up= CC- Take spinneret annulus thickness T microns Take spinneret annulus diameter S microns Assuming spinning conditions are chosen so that the tube wall thickness immediately leaving the annulus is the same as the annulus width, we have length of Volume content within the tube close to the spinneret of length To meet required conditions for stability these two volumes for unit mass of tube must be substantially equal.

hence 15 Example 1 Desired final spun denier= Wind up speed=1250 metres/minute Desired Wall thickness=4 /2 microns Annulus width=140 microns Polymer density=1.33 g./ cc.

Annulus diameter required S microns 16,500 microns= 1.65 cm.

2 as volume required=VZ g2 cos/minute Where V is wind up speed in metres/minute but w :10 n '4 cm m m i 2 gas volume-:V ZXfi cos/minute Example 2 volume 1000 250 324 1.33 X TI'X 4 =8,7,00 cos/minute annulus diameter required The volume of gas required= Example 3 600 X 50 X 10 9X 1.33X11'X-42 50,000 microns 5 ems.

1,000 600 m- 12,500 COS/11111111138 Annulus diameter required= Air quantity= N.B.--Dimensions calculated by this method are optimum but some departure can be made without instability. It is preferable to hold within of the calculated annulus dimension.

The polymer in the samples is polyethylene terephthalate homopolymer which is spun substantially as set out in experiment 6.

What I claim is:

1. A process for the manufacture oiyarn-like structures from fiber-forming synthetic linear polymers selected from the group consisting of nylon, polyester and copolyesters based on terephthalic acid, and stereospecific polypropylene comprising: extruding thepolymer in the form of a thin-walled tube through a substantially annular aperture; introducing a gas supply into the tube; and Winding the tube at a speed which is so related to the dimensions of the annulus, the rate of introduction of the gas and the final desired denier of 25 to 150, that the final wall thickness does not exceed 8 microns, the introduction of the gas being at such a rate that the gas contained within any finite portion of the tube is of substantially the same volume as that contained within any other portion of the tube of the same total weight as said first portion, due allowance being made for Variation of temperatures and expansion of the gas during the process the diameter of the annulus (S) being related to the process variables by the expression and the volume of the gas (G) introduced into the tube being related to the process variables by the expression where w is the desired denier of the extruded tube, grams/9000 meters T is the spinneret annulus thickness, microns d is the density of the polymer, grams/cc.

t is the wall thickness of the extruded tube and does not exceed 8 microns v is the tube windup speed, meters/min.

1r is a constant, 3.1415.

2. A process according to claim 1 wherein the gas is introduced at a rate such that after solidification of the tube no inflation of the tube to a diameter greater than that of the annular aperture takes place.

3. A process according to claim 1 wherein the gas is introduced at a rate sufiicient to prevent any substantial contraction of the tube.

4. A process according to claim 1 in which the tube wTX l0 drrt and the volume of the gas (G) introduced into the tube being related to the process variables by the expression w is the desired denier of the extruded tube, grams 9000 meters T is the spinneret annulus thickness, microns d is the density of the polymer, grams/ cc.

t is the wall thickness of the extruded tube and does not exceed 8 microns v is the tube windup speed, meters/min.

1r is a constant, 3.1415.

References Cited in the file of this patent UNITED STATES PATENTS 1,464,048 Rousset Aug. 7, 1923 2,943,356 Rasmussen July 5, 1960 2,965,925 Dietzsch Dec. 27, 1960 FOREIGN PATENTS 108,284 Pakistan Oct. 3, 1958 1,185,964 France Feb. 16, 1959 

1. A PROCESS FOR THE MANUFACTURE OF YARN-LIKE STRUCTURES FROM FIBER-FORMING SYNTHETIC LINEAR POLYMERS SELECTED FROM THE GROUP CONSISTING OF NYLON, POLYESTER AND COPOLYESTERS BASED ON TEREPHTHALIC ACID, AND STEREOSPECIFIC POLYPROPYLENE COMPRISING: EXTRUDING THE POLYMER IN THE FORM OF A THIN-WALLED TUBE THROUGH A SUBSTANTIALLY ANNULAR APERTURE; INTRODUCING A GAS SUPPLY INTO THE TUBE; AND WINDING THE TUBE AT A SPEED WHICH IS SO RELATED TO THE DIMENSIONS OF THE ANNULUS, THE RATE OF INTRODUCTION OF THE GAS AND THE FINAL DESIRED DENIER OF 25 TO 150, THAT THE FINAL WALL THICKNESS DOES NOT EXCEED 8 MICRONS, THE INTRODUCTION OF THE GAS BEING AT SUCH A RATE THAT THE GAS CONTAINED WITHIN ANY FINITE PORTION OF THE TUBE IS OF SUBSTANTIALLY THE SAME VOLUME AS THAT CONTAINED WITHIN ANY OTHER PORTION OF THE TUBE OF THE SAME TOTAL WEIGHT AS SAID FIRST PORTION, DUE ALLOWANCE BEING MADE FOR VARIATION OF TEMPERATURES AND EXPANSION OF THE GAS DURING THE PROCESS THE DIAMETER OF THE ANNULUS (S) BEING RELATED TO THE PROCESS VARIABLES BY THE EXPRESSION 